Signaling system



June 14, 1932.

P. B. MURPHY SIGNALING SYSTEM Filed Nov. 6, 1928 /NVEN 70R f. 5f MURPHYA 7' TORNE) Patented June 14, 1932 UNITED STATES PATENT oFFIcE PAUL B.MURPHY, OF NYACK, NEW YORK, ASSIGNOR TO BELL TELEPHONE LABORA- TORIES,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK SIGNALINGSYSTEM Application filed November 6, 1928.

This invention relates to signaling systems and particularly to signaltransmission for telephone systems.

An object of the invention is to improve the efiiciency and decrease thecost of signal transmitting systems employing signal currents within thevoice frequency range.

Heretofore, impulses consisting of damped trains of oscillations havebeen employed as signals. Such trains of oscillations were generated byalternately connecting direct current battery to and disconnecting itfrom a tuned circuit including inductance and capacity.

A feature of this invention is a system comprising two differently tunedcircuits of this type having different damping characteristics and socoupled that the output waves or trains of oscillations of one circuithaving the desired frequency are sustained for the required interval bythe other circuit which has a lower damping factor. Signals may beproduced in this manner having such fundamental duration, amplitudecharacteristics and frequency as to make them suitable for transmissionas dialing impulses to control automatic switches or as supervisorysignals over long lines.

Another feature is a circuit arrangement in which the signals areautomatically varied in duration and in rate of transmission.

Another feature is an arrangement whereby the duration of the signals ischanged with the rate of transmission, that is, each rate oftransmission corresponds to a certain duration period of the indivdiualsignals transmitted at said rate.

The invention has been illustrated in the accompanying drawing in whichtwo tuned circuits are arranged tobe controlled by a dial or a lowfrequency source, for production of dial pulses or supervisory impulsesrespectively.

The dial 1 is arranged with its contacts in acircuit including thewinding of relay 2 and resistance 3 connected to a source of directcurrent. A relay 5 is provided to change this circuit to exclude thedial contacts and include connections to ground and alternating currentsource 6. The first tuned Serial No. 317,584.

circuit which comprises a capacity 7 and inductance 8 extends throughthe armature and front contact of relay 2. This tuned circuit is coupledthrough the condensers 9 and 10 to the second tuned circuit. The secondtuned circuit comprises a capacity 11 and inductance 12, and anon-inductive resistance 13 and is coupled through the resistance 14 andprimary windings of the transformer 16 to the output circuit 17. Relay 5besides controlling the impulsing means normally shunts, through itslower armature and back contact, the non-inductive resistance 13 in thesecondtuned circuit and when actuated includes this resistance in thesecond tuned circuit and shunts the condenser 10 in the coupling betweenthe first and second tuned circuit.

It is now assumed that impulses are to be produced by the operation ofdial '1 for transmission over the output circuit 17 as dialing impulses.The first tuned circuit which is employed as the source of the signalsor trains of oscillations is normally connected with the direct currentpath from battery through resistance 4, armature and back contact ofrelay 2, capacity 7 to ground. A charge is therefore normally maintainedon the condenser 7. When the dial is operated a circuit is completedeach time the pulse contacts are opened for the operation of relay 2over a circuit from battery, resistance 3, upper outer armature and backcontact of relay 5, winding of relay 2, upper inner armature and backcontact of relay 5, offnormal contacts of dial 1 toground. Con-(sieqpently relay 2 follows the pulsing of the It should now be observedthat each time relay 2 is operated the condenser 7 will dischargethrough the first tuned circuit by the closing of this circuit throughthe armature and front contact of relay 2. A series of damped waves or atrain of oscillations is thereby set up in this circuit. The dampingfactor of this circuit is determined by the characteristics of theelements 7 and 8 and in this arrangement it may be assumed for the sakeof illustration that these characteristics are such that a train ofoscillations having a frequency of 500 cycles per second is produced inthe circuit. These oscillations are effective to produce oscillations inthe second tuned circuit through the coupling condensers 9 and 10 by thealternate charging and discharging thereof into the second circuit.Signals produced in the second circuit are transmitted through repeatingcoil 16 to the output circuit 17.

It is a well known phenomenon that two oscillatory circuits will producea fundamental frequency and component frequencies and that the componentfrequencies may be both of a higher and a lower frequency than thefundamental frequency. If now as in this case, a second tuned circuit iscoupled to a first tuned circui it is evident that this second circuitcan be made to oscillate at a fundamental frequency which may be of thesame frequency as that of a component frequency of the first circuit,for example a component frequency that is higher than the fundamentalfrequency of the first circuit. To accomplish a result of this naturethe characteristics of the elements 11 and 12 in the second circuit havebeen made, or may be made for the sake of illustration, such that the prduced trains of oscillations have a frequency of approximately 1000cycles per second. In other words, this second circuit will produce afundamental frequency corresponding to a higher component or the secondhigher harmonic of the fundamental frequency of the first ci 'cuit. Itshould be understood that 500 cycles per second as a fun damentalfrequency for the first circuit and 1000 cycles per second as afundamental frequency for the second circuit have been merelyarbitrarily mentioned for the sake of illustration and because currentsof 1000 cycles per second frequency are particularly suitable assignaling currents in telephone circuits. It should, however, beunderstood that this invention is not primarily concerned with the exactvalue of the frequencies in these two circuits but rather with theemployment of tuned circuits of the character that may produce an outputfrequency suitable for dialing and signaling in telephone systems. Forfurther reference in regard to the principles involved in coupledcircuits of this nature, reference may be had to the patents to StoneNo. 726,368 of April 28, 1903, and 726,476 of April 28, 1903.

Another reason for employing two tuned circuits of the characterdescribed to secure signals having the desired frequencies-is to producesignals that at the same time are of such duration, strength andamplitude characteristics as to make them desirable for signalingpurposes as will hereinafter be described.

Relating to the length or duration of each train of oscillations in atuned circuit, it is well known in the art that this depends on thedegree of damping in such a circuit. It is also well known in the artthat with commercial apparatus employed in circuits of the type shown inthe drawing for the generation of trains of damped oscillations, thedamping factor is relatively high. It is also well known that thedamping factor controls the total number of oscillations in any onetrain. it is apparent therefore that each train will be of a longerduration when the generated frequency is low than it would be when thegenerated frequency is high. Therefore, in order to secure oscillationsin the output circuit 17 that are suiiiciently sustained to serve assignals, the first circuit is damped as low as can be obtainedpractically and tuned to resonate at a lower frequency than thefrequency desired for the output signals. In the example cited, 500cycles per second has been arbitrarily mentioned for the sake ofillustration as the fundamental frequency for the first circuit, whereas1000 cycles per second has been considered as the desirable outputsignal frequency for the second circuit. I Having obtained longsustained trains of oscillations in the first circuit, the outputsignals of the desired frequency in the second cir cuit may be sustainedfor an even longer period of time, by making the coupling between thetwo circuits rat-her loose, that is, the condensers 9 and 10 of smallcapacity, permitting a lower degree of damping to be maintained in thesecond circuit than in the first. Relating to the securing of outputsignals of the proper amplitude, it is desirable to further adjust thevalues of the tuning elements, condensers 7 and inductance 8' of thefirst circuit and the energy supply therefor through resistance 4;. sothat the effective voltage variations in the second circuit are such asto produce trains of oscillations of the desired amplitude. In otherwords, the capacity of condenser 7 is comparatively large and theresistance of the inductance element 8 comparatively small. With thisarrangement the high amplitude of the fundamental frequency of the firstcircuit will naturally tend to produce oscillations in the secondcircuit of considerable amplitude even though the coupling between thecircuits is rather low.

However, the trains of oscillations produced in the above manner in thefirst circuit are likely to have the efiect that the first few waveswill have an amplitude beyond that acceptable for the desired signal.The loose coupling on the other hand prevents these peaks from afiectingthe second circuit. That is, the capacity of the coupling condensers issuch that the energy of the first few oscillations of the fundamentalfrequency of the first circuit will not be fully effective to produceoscillations of an objectionable amplitude 1n the second clrcuit, whllethe amplitude of the succeeding oscillations in the first circuit willbecome more fully effective as the capacity of the condensers 9 and 10is adequate in this respect. Hence, the train of oscillations producedby the second circuit will have more gradually decreasing ampli-' tudesthan the waves in the first circuit and thereby make them more suitablefor output signals.

When, therefore, these circuits are operated through dial 1, outputsignals are produced at 17 having duration and amplitude characteristicsparticularly suitable for dialing impulses for use in automatictelephone systems. It should be understood that these impulses aresustained and are of such an amplitude that they will be effective forthe desired period of signaling even though the amplitude is graduallydecreasing towards the end of this period. The effective period shouldalso be so proportioned in this respect that when it comes to an end theimpulses will have decreased in amplitude to such an extent that theywill cease to have any further effect on the apparatus that they areintended to control. If the impulses are so controlled they will providesharply defined operating impulses equivalent to alternating currentimpulses or direct current impulses.

This system is also arranged for the transmission of signals that may beused, for ex ample, as supervisory signals in telephone systems. Signalsof this type may, of course, be sent out at a faster rate than dialimpulses but be of the same general character, that is, the impulses maydecrease in amplitude more rapidly and hence be shorter in duration asfar as their effectiveness is concerned.

For this purpose the non-inductive resist ance 13 is inserted in thesecond circuit and one of the coupling condensers, condenser 10, isshort-circuited under control of relay 5. As the length of the trains ofoscillations in the second circuit depend on damping effects and dampingmay be increased by increasing the resistance in this circuit, itfollows that by allowing resistance 13 to remain in the second circuit,more sharply damped output signals will be produced, to wit, signals ofa shorter duration. It also follows that by short-circuiting condenser10 the second circuit will assume more nearly the dampingcharacteristics of the first circuit. Therefore the trains ofoscillations will have a still shorter duration.

When supervisory signals are to be transmitted relay 5 is operated inany suitable manner. This causes the resistance 13 to be inserted in thesecond circuit through the opening of the short circuit through thelower armature and back contact of relay 5 and, due to the closing ofthe connection through the lower armature and front contact, condenser10 is short-circuited. The connections for controlling the relay 2 bythe dial 1 are also opened at the upper armature and having a frequencyof, for example, 20 cycles per second, which is generally adopted as therate at which supervisory signals are transmitted. Hence, relay 2 willnow be alas to produce alternating current impulses ternately operatedand released 20 times per second by current from source 6 through theouter upper armature and front contact of relay 5, winding of relay 2,inner upper armature and front contact of relay 5 to ground. Outputsignals at this rate are now therefore produced in the same manner aswhen the dial is operated as hereinbefore described, exceptthat due tothe short-circuiting of the condenser 10 and the insertion of resistance13 these signals will be shorter in duration and of a lower initialamplitude. The duration and the effective amplitude will be such as tomake these signals suitable for supervisory purposes.

'VVhen, therefore, the system chosen to illustrate this invention isused to transmit dialing impulses, such impulses are pro duced to bear acertain relation in duration and amplitude to the rate at which the dialis operated, whereas when the system is used to produce supervisoryimpulses said im pulses bear a certain other relation in regard to theduration and amplitude to the rate at which they are transmitted. Whenthe rate of transmission is low, the signals are effective for longerperiods than when the rate of transmission is high.

It should be understood that while the invention has been illustrated inconnection with a given circuit arrangement, it is readily adaptable toother systems without departure from the spirit thereof and that theinvention should only be limited by the scope of the appended claims.

What is claimed is:

1. In a signaling system a circuit tuned to a given frequency ofoscillation, a second circuit tuned to a different frequency ofoscillation, means for coupling said circuits, en-, ergizing means,means for applying said energizing means to said first circuit at aplurality of different rates to produce corresponding trains ofoscillations in the second circuit, means to determine the rate at whichsaid energizing'means is applied to said first circuit, and meanscontrolled by said determining means for changing the dampingcharacteristics of said second circuit.

2. In a signaling system a circuit tuned to a given frequency ofoscillation, a second cirrality of different rates to producecorresponding trains of oscillations in the second circuit, means todetermine the rate at which said energizing means is applied to saidfirst circuit, and a resistance controlled by said determining means forchanging the dam; ing characteristics of said second circuit.

3. A signaling system comprising two tuned circuits, a source ofcurrent, means for associating said source with one of said cir cuitsperiodically at diflerent rates of occurrence to produce in said circuittrains of oscillations, coupling means between said circuits to producetrains of oscillations in the second circuit in response to trains ofoscillations in the first circuit, and means controlled by said firstmentioned means for changing the damping characteristics in the secondcircuit for the trains of oscillations produced thereby.

4. A signaling system comprising two tuned circuits, a source ofcurrent, means for associating said source with one of said circuitsperiodically at diiierent rates of occurrence to produce in said circuittrains of oscillations, coupling means between said circuits to producetrains of oscillations in the second circuit in response to trains ofoscillations in the first circuit, means for changing the dampingcharacteristics in the second circuit for the trains of oscillationsproduced thereby so that the damping characteristics at any certain timebear a certain relation to the rate at which trains of oscillations areproduced in the first circuit at that time.

5. A. signaling system comprising a tuned circuit for producing trainsof oscillations of comparatively high amplitude, another tuned circuitfor producing trains of oscillations of similar amplitude but of ahigher frequency, a source of current, means for associating said sourcewith the first mentioned circuit periodically to produce in said circuittrains of oscillations of said high amplitude and at different rates ofoccurrence, coupling means between said circuits to produce trains ofoscillations in the second circuit in response to trains of oscillationsin the first circuit, said coupling means being comparatively loose sothat the first few oscillations 01": each train of the first circuitcannot be fully effective in the production of trains of oscillations inthe second circuit in regard to amplitude, and means for sustaining saidtrains or" oscillations in said second circuit for a longer period thanthe trains of oscillations in the first circuit and for regulating saidperiod to bear a certain relation to the rate at which the trains ofoscillations are produced in the first circuit.

6. In a system for producing and transmitting trains of oscillations,the method comprising producing said trains of oscillations in twostages, increasing the rate of transmitting the trains of oscillationsin the first stage, and simultaneously increasing the damping of saidtrains of oscillations in the second stage.

In witness whereof, I hereunto subscribe my name this 3rd day ofNovember 1928.

PAUL B. MURPHY.

